I got my Ban'thalos after sitting on said tree for about a week or so and logging in every now and then. Eventually I saw him up when I logged and a mage was trying to kill it with slow fall and what have you. He failed to pull Ban'thalos all the way down and the mob reset while the mage went out of range. I placed my trap, pulled and tamed. Got called a ninja because of it. *shrug*

I do not support killing a player or their tame if they are already in progress of taming. Or killing the player and taming the mob yourself if they were there first and already engaged. However, if the player is let to attempt their tame and they fail on it on their own and the mob resets, then I think it's fair game to whoever engages it first.